1. Field of the Invention
This invention relates generally to position determination of a flying object. More particularly, the present invention relates to a method and apparatus for optically determining an instantaneous spatial position of a spherical flying object such as golf ball or tennis ball.
2. Description of the Prior Art
Quite often, golfers perform exercise using a golf exercising machine or playing in a golf exercising facility whose space is limited. In such a case, it is difficult for the golfer to know how the hit ball is actually carried due to the limited space of the machine or facility. It then becomes necessary to determine an instantaneous spatial position of the hit ball and to process the thus determined ball position for calculating the vertical trajectory angle or horizontal trajectory angle (lateral deviation angle) of the hit ball, thereby providing an approximate ball flying path. Further, even if there is an ample space for hitting a ball over a full flying distance, it is sometimes preferable for stroke checking to know the trajectory angle of the hit ball.
Conventionally, there are various methods for determining an instantaneous spatial position of a hit ball.
A first conventional method utilizes a multiplicity of cords arranged to cover a flying path region for a hit ball and respectively connected to electric switches. In this method, a hit ball is caused to impinge particular one of the cords, thereby actuating a corresponding switch.
However, the first method is defective in that the ball flying path is unacceptably obstructed by the cords. Further, the cords may be damaged by repetitive contact with the ball. Moreover, the ball may come into improper impingement with a cord, consequently failing to provide intended detection.
A second conventional method utilizes a multiplicity of photoelectric switches arranged to cover a flying path region for a hit ball. In this method, a particular one of the photoelectric switches is actuated when light input for that particular switch is cut off by passage of the hit ball.
However, the second method is disadvantageous in that a great number of photoelectric switches are necessary to increase the resolution of detection and/or to optically cover a wide flying path region.
In a third conventional method, use is made of an oscillating mirror or rotary polygon mirror combined with a lens system for generating scanning laser beams which are made to repetitively translate in a scanning plane. A hit ball is made to pass through the scanning plane, and beam cut-off timing is measured to determine an instantaneous spatial position of the hit ball.
The third method relies on mechanical movement of the oscillating mirror or rotary polygon mirror, and such mechanical movement inevitably provides irregularities for scanning translational movement of the laser beams. Further, the mechanical movement of the mirror may be also affected by the environmental conditions such as temperature, humidity and so on. Thus, the third method cannot necessarily provide accurate position determination.
A fourth conventional method utilizes a video camera for directly taking an image of a flying ball. In this method, an instantaneous position of the ball is directly determined by image measurement.
However, the fourth method is defective in that two different ball positions on the same sight line of the video camera provides the same image position, consequently resulting in erroneous position detection. Further, a relatively small number of picture elements are assigned for a ball image, so that there is also a problem in image resolution.